cheapr (version 1.2.0)

copy: Copy R objects

Description

shallow_copy() and deep_copy() are just wrappers to the R C API functions Rf_shallow_duplicate() and Rf_duplicate() respectively. semi_copy() is something in between whereby it fully copies the data but only shallow copies the attributes.

Usage

shallow_copy(x)
semi_copy(x)
deep_copy(x)

Value

A shallow, semi or deep copied R object.

Arguments

x

An object to shallow, semi, or deep copy.

Details

Shallow duplicates are mainly useful for adding attributes to objects in-place as well assigning vectors to shallow copied lists in-place.

Deep copies are generally useful for ensuring an object is fully duplicated, including all attributes associated with it. Deep copies are generally expensive and should be used with care.

semi_copy() deep copies everything except the attributes. This is experimental but in theory should be much more efficient and generally preferred to deep_copy().

To summarise:

• shallow_copy - Shallow copies data and attributes

• semi_copy - Deep copies data and shallow copies attributes

• deep_copy - Deep copies both data and attributes

It is recommended to use these functions only if you know what you are doing.

Examples

library(cheapr)
library(bench)
df <- new_df(x = sample.int(10^4))

# Note the memory allocation
mark(shallow_copy(df), iterations = 1)
mark(deep_copy(df), iterations = 1)

# In both cases the address of df changes

address(df);address(shallow_copy(df));address(deep_copy(df))

# When shallow-copying attributes are not duplicated

address(attr(df, "names"));address(attr(shallow_copy(df), "names"))

# They are when deep-copying

address(attr(df, "names"));address(attr(deep_copy(df), "names"))

# Adding an attribute in place with and without shallow copy
invisible(attrs_add(df, key = TRUE, .set = TRUE))
attr(df, "key")

# Remove attribute in-place
invisible(attrs_add(df, key = NULL, .set = TRUE))

# With shallow copy
invisible(attrs_add(shallow_copy(df), key = TRUE, .set = TRUE))

# 'key' attr was only added to the shallow copy, and not the original df
attr(df, "key")